The present invention relates to hydrostatic transaxle assemblies, and more particularly, to such assemblies which are used as the sole means of propulsion for the wheels of a vehicle.
Certain vehicles, such as lawn and garden tractors, have used hydrostatic transaxle assemblies for transmitting engine torque to a pair of ground-engaging drive wheels to propel the vehicle A typical transaxle assembly which has been used commercially includes a variable displacement hydraulic pump, such that the ratio of pump output flow to pump input speed (engine speed) may be infinitely varied by the vehicle operator. This ability to infinitely vary the output-input ratio, without interrupting torque transmission, makes such transaxle assemblies preferred over conventional clutch and gear transmissions for vehicles such as lawn and garden tractors.
Vehicles which have utilized hydrostatic transaxles have sometimes been equipped with "wheel brakes", i.e., a pair of brakes, with one located at the end of each axle shaft, adjacent its respective wheel. There are several disadvantages of the typical wheel brake arrangement, one of which relates to the amount of control linkage required to actuate two axially spaced apart wheel brakes from a single brake pedal. Another problem relates to the fact that the braking action is being applied at a location in the power path where the speed of rotation is at a minimum, and the torque being transmitted is at a maximum. As a result, a greater amount of braking torque is required, thus making it more difficult to achieve the desired durability of the various components of the braking mechanism.
A brake mechanism for a hydrostatic transaxle of the general type to which the present invention relates is illustrated and described in U.S. Pat. No. 4,696,164, assigned to the assignee of the present invention. In the referenced patent, there is illustrated a cam-ramp and friction clutch mechanism which permits the vehicle operator to select among normal operation, operation in a locking differential mode, and a brake mode of operation. Hydrostatic transaxles including the mechanism illustrated and described in the referenced patent have been sold commercially by the assignee of the present invention. Although the locking differential and braking mechanism of the referenced patent performs in a satisfactory manner, it does add substantial structure, complication, and expense to the transaxle assembly.